/Engine/Source/Runtime/Media/Public/IMediaCache.h
This method can be used to probe a media player's decoder for which samples are scheduled for loading, being loaded, or finished loading. This is generally only supported by those players that expose some kind of internal sample caching or load/decode scheduling mechanism, and most players may simply ignore this call.
true on success, false if not supported.
virtual bool QueryCacheState ( EMediaCacheState State, [TRangeSet](API\Runtime\Core\Math\TRangeSet)< [FTimespan](API\Runtime\Core\Misc\FTimespan) > & OutTimeRanges ) const